Contrast-enhanced mammography may be used to image the diffusion of blood in interstitial tissue of malignant lesions or tumors. Contrast-enhanced Mammography (CEM) images can be acquired through 1) a temporal sequence of acquisitions using a single x-ray spectrum followed by image subtraction (Temporal-CEM); 2) through a dual or multi-energy sequence using several x-ray spectra followed by recombination of images acquired with different spectra (CESM); or 3) through a temporal sequence of a dual or multi-energy sequence using several x-ray spectra followed by recombination of images acquired with different spectra (Temporal-CESM).
FIG. 1 shows an exemplary Temporal-CEM acquisition process where a pre-injection image (mask image) is acquired using a single x-ray spectrum, followed by an intravenous (IV) injection of a contrast agent, and the acquisition of a series of post-injection images. The pre-injection and post-injection images may typically be acquired with a high energy spectrum compared to a conventional or low energy spectrum typically used in x-ray imaging of the breast (e.g., mammography, digital breast tomosynthesis). The mask image is then log-subtracted from each of the post injection images in order to provide a series of contrast agent images.
FIG. 2 shows an exemplary CESM acquisition process where, after an IV injection of a contrast agent, a series of images are acquired with high energy and low energy x-ray beams. The images acquired at different energies are paired and then recombined to produce a contrast-agent equivalent image, also shown as a “DE” image.
Referring to FIG. 3, a variation of the CESM process, referred to as Temporal-CESM, is illustrated where the high and low energy acquisition process is repeated several times after injection of a contrast agent to deliver a series of DE images that monitors the passage of the contrast agent through anatomical structures of a breast seen under a given incidence and geometry, or to deliver a series of images of one or several breasts under several incidences and/or geometries.
Turning to FIG. 4, assuming the patient's breast is stationary, a series of only high energy images may be acquired over time and the previous low energy images may be used to perform the recombination in order to reduce the x-ray dose delivered to the patient. In cases where the breast may not be stationary, a registration algorithm may be utilized to conform each high energy image to the same reference as the corresponding low energy image.
However, in each of these techniques, because the images are acquired at least a few minutes after IV injection of the contrast agent, the contrast agent is diluted in the patient's blood, and vessels feeding any tumors may not be visible. This is a disadvantage because observing the vessels feeding the tumors provides valuable clinical information. There is ample evidence that the overall vascularity of a tumor is an indicator of the tumor type and grade, but distinguishing between arteries and venous vessels in an image to determine the overall vascularity is often hindered due to the distribution of the contrast agent in the vasculature and the loss of temporal information provided by a first-pass of the contrast agent.
Furthermore, correlation between images acquired during the arterial phase and images acquired during the diffusion in interstitial tissue requires maintaining the breast in the same or similar geometry and position with respect to the imaging components (i.e., x-ray tube and detector). However, the arterial and diffusion phases may be separated by several minutes during which a patient may move, and breast compression may reduce patient comfort and may affect diffusion of the contrast agent in the breast. In addition, operations and procedures by a technologist performing the breast positioning, contrast agent injection, and image acquisition may vary, and those variations may reduce the quantitative content of the acquired images.
There is a need for techniques and devices that enable fast acquisition of high resolution images of an injected breast, and that enable the imaging of the vessels feeding tumors during the arterial phase, with the ability to follow the contrast agent uptake over time.